This invention relates to a method for forming a metal layer with a positive pattern on a substrate.
It has been known in the prior art that such a metal layer with pattern may be formed by partially electroless plating or by etching of a metal-clad substrate.
Partially electroless plating comprises the steps of:
printing a desired pattern on a substrate with an agent which can prevent metal deposit by electroless plating, carrying out electroless plating on the substrate, and PA1 carrying out electrolytic plating on the electroless plating layer. PA1 coating the metal with a photosensitizer; PA1 exposing the photosensitizer to actinic radiation through a positive or negative with a desired pattern; PA1 washing the exposed area (if a positive is used) or the unexposed area (if a negative is used); and PA1 removing the metal layer, on which the photoresist is not present, by etching it using a strong acid or strong alkali. PA1 (a) The water-soluble ink is not completely bonded to the resinous material. Therefore, the contours of the resulting metal layer are not sharp. PA1 (b) Water remains in the ink layer after it has been coated on the resin. The water disturbs the metallizing operation under vacuum.
However, this method has the defect that electric current concentrates at the border-line portion of the electroless plating layer during electrolytic plating, whereby metal deposits in the form of needles or grains are formed. To avoid this defect, it is necessary that the metal layer be made relatively thin. However, making the metal layer thin reduces the durability of the substrate. Furthermore, the kinds of substrates which may plated are limited.
The prior art method for etching a metal-clad substrate comprises the following steps:
Depending on the etching method, it is necessary to treat the acidic or alkaline waste so as not to cause water or air pollution. Furthermore, the photoresist must be removed in order to use the resulting substrate for decorative purposes.
U.S. Pat. No. 3,935,334 issued on Jan. 27, 1976 based on an application filed by Narui et al discloses a process for producing a metallized resin film for a condenser element comprising at least one dielectric resinous layer and at least one metal deposition layer, wherein the improvement comprises forming on said resinous layer a margin wherein the metal deposition layer is not present by the steps comprising
1. providing a water-soluble coating layer by applying a water-soluble paint to at least one side of the dielectric resinous layer in the portion of the resinous layer corresponding to the pattern of margin, PA0 2. providing a metal deposition layer on the dielectric resinous layer partially coated with the water-soluble coating layer, said metal deposition layer being applied by means of vacuum metallizing procedures, and PA0 3. removing the water-soluble coating layer and the metal deposition layer thereon by dissolving away the water-soluble coating layer with water.
The process of Narui et al has the following defects: